Combined scan and track antennas

ABSTRACT

Combined scan and track antennas are disclosed, each comprising a reflector and a feed thereto in which the track reflector and its feed and the feed to the scan reflector are all fixed with respect to each other and the scan reflector rolls in such a manner that a line through the center of the spherical feed antenna and the fixed feed point therefor always is perpendicular to a point on the surface of the spherical reflector through which it extends.

United States Patent 7 Anderson et al.

[54] COMBINED SCAN AND TRACK ANTENNAS Inventors: Harold Anderson,Phoenix, Jerry Blanchard Cain; John G. Doggett, Jr., both of Scottsdale,all of Ariz.

Assignee: Motorola, Inc., Franklin Park, 111.

Filed: Jan. 15, 1971 Appl. No: 106,792

[52] US. Cl. ..343/76l, 343/725, 343/757,

343/756, 343/777 Int. Cl. ..H01q 3/12 Field of Search ..343/757, 758,761, 779, 839,

References Cited UNITED STATES PATENTS v 7/1968 Williams et al...343/840X [451- Oct. 3, 1972 3,530,476 9/ 1 970 Ravenscroft ..343/76l2,489,865 11/1949 Cutler ..343/839 X 2,570,197 10/1951 Bohnert et al...343/839 X Primary Examiner-Herman Karl Saalbach AssistantExaminerSaxfield Chatman, Jr. Attorney-Mueller & Aichele [5 7] ABSTRACTCombined scan and track antennas are disclosed, each comprising areflector and a feed thereto in which the track'reflector and its feedand the feed to the scan reflector are all fixed with respect to eachother and the scan reflector rolls in such a manner that a line throughthe center of the spherical feed antenna and the fixed feed pointtherefor always is perpendicular to a point on the surface of thespherical reflector through which itextends.

11 Claims, 3 Drawing Figures PATENTEDnm m2 SHEET 1 (IF 2 INVENTOR Ham/dAnderson ubrry B/ana/m'd Cain BY Joli/7 G. Doggef/ Jr.

SHEET 2 BF 2 W (Z v INVENTOK Harold Anderson Jerry Blane/1am Cain Y JohnG. Doggefl Jr W W Fl Arrr's.

BACKGROUND This invention concerns itself with a combined scan and trackantenna.

It is known to transmit a radio wave in a scanning manner and to pick upthe waves reflected from an object by a tracking antenna. The scanningantenna may involve moving parts which may move in a manner which isdifferent than a manner of moving the tracking antenna, in the processof tracking the object which may be illuminated by the scan antenna.When the scan and track antennas are both mounted on a vehicle such asan airplane, it may be advantageous to fix the track antenna to thevehicle and point the vehicle at the object. To save room and to makesure that the object is in the area that is scanned, the scan antennashould also be mounted on the vehicle and should be placed as nearlycoincident with the positioning of the track antenna as is possible. Itis known to place two grid type antenna reflectors one inside the otherand with the grids properly oriented with respect to each other and withappropriate polarization of the feeds thereto, to provide antennapatterns produced by the two antennas which are essentially independent.Therefore, one of these two antennas may be used as a scan antenna andthe other thereof may be used to track an object in the same area. Whilethe two reflectors are usually parabolic, they can be either bothparabolic or both spherical or one thereof can be parabolic and theother can be spherical. For feeding a spherical reflector, the feed orfocus point is at a point one half way from the surface of the reflectorto the center of the sphere of which it is a part. For a sphericalscanning reflector to provide scanning, the reflector being stationary,the feed point must move in a sphere which is concentric with thespherical reflector and which has a radius equal to one half of theradius of the spherical reflector, this concentric sphere being called afocus sphere of the spherical reflector. Several ways are known toaccomplish this result, one of which is to hinge a wave guide feed meansat the center of the spherical reflector, the end of the wave guidepointing towards the spherical reflector and the length of the waveguide from the hinge point to its end being about equal to one half theradius of the spherical reflector. This requires much space in front ofthe spherical reflector and furthermore the end of the feed means doesnot move in the focus sphere but in an approximation thereof. Anotherknown manner in which this moving of the feed means in a focus sphere isattempted comprises the use of a complicated hinged feed line havingseveral, three for example, hinged joints in the feed wave guide, whichcauses the mouth of the wave guide to move more nearly in the focussphere. This known method requires complicated hinged feed line meansand complicated means to operate the feed line to cause proper scanning.

It is an object of this invention to provide an im' proved combined scanand track antenna.

It is a further object of this invention to provide a combined scan andtrack antenna which is simpler and easier to make than known combinedscan and track antennas.

It is still a further object of this invention to provide combined scanand track antennas involving a minimum number of moving parts.

SUMMARY In accordance with this invention, the track antenna includes areflector and a feed means which are fixed with respect to each otherand in which the scan antenna includes a scan reflector and a feed meanstherefor and in which the feed means to the scan reflector is fixed withrespect to the track antenna and in which the scan reflector of the scanantenna rolls on a guide surface which is fixed with respect to thetrack reflector in such a manner that the feed for the scan reflector isalways the distance of one half the radius of the scan reflector fromthe scan reflector and also directs a beam on a line through the centerof the feed for the scan reflector which is perpendicular to the surfaceof the scan reflector. That is, while the scan reflector is rolling, thefixed feed means for the scan reflector-is always at a focus point forthe rolling scan reflector.

DESCRIPTION The invention may be better understood upon reading thefollowing description in connection with the accompanying drawing inwhich FIG. 1 illustrates a combined scan and track antenna whichembodies the invention,

FIG. 2 illustrates a modification of the antenna of FIG. 1 and FIG. 3 isa fragmentary sectional view of FIG. 2 on line 3-3 thereof.

In FIG. 1, the track antenna comprises a parabolic reflector l0 and afeed or pick up means therefor comprising a Cassegranian reflector 12held in position at the focus of the parabolic reflector 10 as by studs14. A fixed wave guide 16 extends through the vertex of the parabolicreflector l0 and ends so as to radiate energy in the direction of thereflector 12 or to receive energy from the reflector 12. The reflectorl2 reflects the energy in a direction of the reflector 10 or reflectsenergy from the reflector 10 into the wave guide 16. The reflectors 10and 12 may be made of wire mesh and the feed from the wave guide 16, orto it, is polarized in a desired manner so as to prevent interferencewith the radiation of the scan antenna which will be described. Theantenna comprising the elements l0, l2, l4 and 16, and the manner ofmaking it out of wire mesh and of polarizing the feed thereto is wellknown, whereby no further explanation thereof need be provided.

The scan antenna comprises a spherical reflector 18 which is movablewith respect to the track antenna and a feed therefor, comprising a waveguide 20 ending in a horn 22, which are fixed with respect to the trackantenna. The end of the horn 22 is at the focus, that is at a distanceequal to one half the radius of the spherical reflector 18 from thespherical reflector 18. The reflector 18 may be a solid reflector andthe feed by and to the horn 22 is also polarized in such a'manner thatthe scan and track antennas operate substantially independently of eachother.

As is stated above, the reflector 18 is movable in that it rolls on theouter surface of a guide 24. The guide 24 is fixed to the back of thereflector 10, whereby the side adjacent thereto conforms to thereflector 10 in shape. The side of the guide 24 adjacent the movablereflector 18 is spherical in shape and has a radius equal to one halfthe radius of the spherical reflector 18. So that the guide 24 shouldnot shield the reflector 18 from any wave that is travelling towards oraway from the reflector 18, the guide 24 should be made of anonconductive material. Means may be provided to cause the guide 24 andthe reflector 18 to roll with respect to each other without slipping.This means may take any known form as meshing teeth (not shown) in thecontacting portion of the reflector 18 and the guide 24. Or straps 26and 28 may be provided, the strap 26 being fastened to the top of thereflector 18 as viewed in the figure and to the bottom of the guide 24,the strap 28 being fastened between the bottom of the reflector 18 andthe top of the guide 24. Since the straps 26 and 28 are very thin, thereare shown, for convenience, as lines. The straps should not be ofconductive material. A hole 30 is formed in the reflector 18 to clearthe feed wave guide 16 as the reflector 18 rolls on the guide 24. Itwill be seen that as the reflector 18 rolls on the guide 24, the centerC of the spherical reflector 18 moves but the focus point at the horn 22does not move and a line can be drawn from any position of the center Cthrough the fixed focus point at the horn 22 that will be a radius ofthe reflector 18. This is due to the fact that the contact of thespherical reflector 18 and the spherical guide 24 is always at a tangentplane to the two spheres and a line perpendicular to the tangent planeto the two spheres is a radius of both of the spheres. Since all theradii of the sphere 24 passes through the point 22, the line through thepoint of contact of the reflector 18 and the guide 24 which is theradius of the guide 24 is also a radius of the reflector 18. Therefore,in every position of the spherical reflector 18, the point 22 is on aradius thereof and is at a distance equal to one half the distance tothe center of thespherical antenna 18, that is, as the reflector 18rolls, the horn 22 is always at a focus point of the reflector 18- andyet the wave reflected by the reflector is directed in differentdirections by the rolling of the reflector 18. Furthermore, there isnothing physical beyond the wave guide 20 in the direction towards thecenter C, whereby the described structure extends only to the wave guide20 and the described structure is smaller than known combined scan andtrack antennas which extend beyond the focus point 22.

As described, the surface of the guide 24 adjacent the antenna 18 isspherical as is the facing surface of the antenna reflector 18. ifdesired the surface of the guide 24 away from the reflector may becylindrical instead of spherical and the reflector 18 may also becylindrical, resulting in a planar scan rather than the possiblemulti-directional scan where the contacting surfaces of the guide 24 andthe reflector 18 are both spherical.

As noted, in the device of Fig. 1, the guide 24 and the straps 26 and 28should not be of conductive material since they may shield the reflector18 when made of conductive material. As shown in Fig. 2, the roll guides32 and 34 may be behind the reflector 18.

In Fig. 2, elements are given the same reference characters as similarelements of Fig. l. A fixed frame 36 is provided on which the fixed waveguide and the horn 22 and the fixed parabolic reflector 10 may bepositioned as by struts 38 and 40. The roll guides 32 and 34 areidentical and are integrally fixed to the fr e 36. The sha e of onethereof is shown in Fi 3. Tlie roll guide 32 is in the shape of asegment t a cylinder having a radius equal to one half the radius of thespherical reflector 18. The rolling means 42 and 44 are identical andare cylindrically concave and have a radius equal to the radius of thespherical reflector 10. The shape of the rolling means 42 and itsrelation to the rolling guide 32 are shown in Fig. 3. The rolling meansare fixed to support bars 46 and 48 which support the sphericalreflector 18. As the rolling means 42 and 44 roll on the roll guides 32and 34 respectively, the reflector 18 moves in a manner as to keep itsfocus point at the mouth of the antenna horn 22, however waves arescanned in a direction above and below a line through the horn 22 andthe wave guide 16. It is noted that the roll guides 32 and 34 and theroll means 42 and 44 are behind both reflectors l0 and 18, whereby theycan be made of metal. The roll guides 32 and 34 are convex and the rollmeans 42 and 44 are concave, however, if desired they may all be convexand still give the reflector 18 the proper motion.

What is claimed is:

1. Combined antenna means for radiating waves in the same areacomprising a first and a second reflector rollable relative to eachother,

respective feed means for said reflectors, said first reflector and bothsaid feed means being fixed with respect to each other, and

means for rolling said second reflector with respect to said firstreflector.

2. The invention of claim 1 in which said second reflector is sphericalin shape and its respective feed means is positioned to radiate energyin a direction of said second reflector from the focus point of saidsecond reflector.

3. The invention of claim 2 in which said means for rolling includes arolling guide having a spherical surface which has half the radius ofthe second antenna.

4. The invention of claim 3 in which said rolling guide fits on saidfirst reflector in a manner to present its spherical surface to saidsecond reflector.

5. The invention of claim 4 in which means are provided to preventslipping of the second reflector and the rolling guides.

6. The invention of claim 5 in which said first reflector is ofparabolic shape.

7. The invention of claim 1 in which said second reflector iscylindrical in shape and said means for rolling said second antenna withrespect to said first antenna is also cylindrical in shape.

8. The invention of claim 1 in which said second reflector is sphericalin shape and said means for rolling said second antenna with respect tosaid first antenna comprises a pair of means having contactingcylindrical surfaces.

9. The invention of claim 8 in which one of said contacting cylindricalsurfaces is concave.

10. The invention of claim 8 in which at least one of said contactingsurfaces is convex.

1 1. The invention of claim 8 in which said contacting surfaces arelocated in the same direction from both reflectors.

1. Combined antenna means for radiating waves in the same areacomprising a first and a second reflector rollable relative to eachother, respective feed means for said reflectors, said first reflectorand both said feed means being fixed with respect to each other, andmeans for rolling said second reflector with respect to said firstreflector.
 2. The invention of claim 1 in which said second reflector isspherical in shape and its respective feed means is positioned toradiate energy in a direction of said second reflector from the focuspoint of said second reflector.
 3. The invention of claim 2 in whichsaid means for rolling includes a rolling guide having a sphericalsurface which has half the radius of the second antenna.
 4. Theinvention of claim 3 in which said rolling guide fits on said firstreflector in a manner to present its spherical surface to said secondreflector.
 5. The invention of claim 4 in which means are provided toprevent slipping of the second reflector and the rolling guides.
 6. Theinvention of claim 5 in which said first reflector is of parabolicshape.
 7. The invention of claim 1 in which said second reflector iscylindrical in shape and said means for rolling said second antenna withrespect to said first antenna is also cylindrical in shape.
 8. Theinvention of claim 1 in which said second reflector is spherical inshape and said means for rolling said second antenna with respect tosaid first antenna comprises a pair of means having contactingcylindrical surfaces.
 9. The invention of claim 8 in which one of saidcontacting cylindrical surfaces is concave.
 10. The invention of claim 8in which at least one of said contacting surfaces is convex.
 11. Theinvention of claim 8 in which said contacting surfaces are located inthe same direction from both reflectors.